CONNECTIVE TISSUE – CHAPTER CONNECTIVE TISSUE

I. General Concept

Connective tissue is a basic type of tissue found in the body, originating from the mesoderm, playing a crucial role in supporting, protecting, and connecting different tissues and organs.

II. Classification

Based on structure and function, connective tissue is divided into three types:

• Proper connective tissue: Includes types of connective tissue such as loose connective tissue, dense connective tissue, elastic connective tissue, adipose tissue, etc.

• Cartilage: Functions to support, protect, and provide low friction for joints.

• Bone: Functions to support, protect, and provide a framework for the body.

III. General Structure of Connective Tissue

Connective tissue consists of two main components:

• Ground substance: A non-structural matrix, highly viscous, surrounding cells and connective fibers. Ground substance is composed of:

• Glycosaminoglycans (GAGs): Long polysaccharide chains, negatively charged, capable of attracting water and creating viscosity for the ground substance. Some common GAGs include:

• Hyaluronic acid (HA): Found in the umbilical cord, synovial fluid, vitreous humor, and cartilage.

• Chondroitin sulfate (CS): Found in cartilage, bone, cornea, skin, and the wall of the aorta.

• Dermatan sulfate (DS): Found in skin, tendons, and the outer coat of the aorta.

• Heparan sulfate (HS): Found in the wall of the aorta, pulmonary arteries, liver, and basement membrane.

• Keratan sulfate (KS): Found in the cornea, nucleus pulposus, and elastic cartilage.

• Structural glycoproteins: Proteins with attached carbohydrate chains. They play a role in connecting the components of the ground substance, creating structure for the connective tissue. Some important structural glycoproteins include:

• Fibronectin: Synthesized by fibroblasts and epithelial cells.

• Laminin: Synthesized by epithelial and endothelial cells. Laminin mediates the connection between collagen type IV and heparan sulfate, proteoglycans.

• Thrombospondin: Produced by platelets during blood clot formation. Thrombospondin is also synthesized by endothelial cells, fibroblasts, and smooth muscle cells.

• Tissue fluid: Fluid surrounding cells and connective fibers, similar in composition to plasma but with lower protein concentrations.

• Connective fibers: Fibrous structures responsible for supporting, connecting, and providing strength to connective tissue. There are three main types of connective fibers:

• Collagen fibers (reticular fibers): The most common type, white in fresh tissue, stained red in eosin and blue in aniline. The diameter of collagen fibers is about 50nm. Collagen is classified into many types, each with its own unique structure and function.

• Collagen type I: Found in the dermis of the skin, bones, tendons, ligaments, fibrous cartilage, compatible with dermatan sul.

• Collagen type II: Found in hyaline cartilage and elastic cartilage, compatible with chondroitin.

• Collagen type III: Found in reticular fibers in nervous tissue, the stroma of the liver, kidneys, spleen, and lungs.

• Collagen type IV: Found in the basement membrane of the basal lamina.

• Collagen is synthesized by fibroblasts, osteoblasts, chondroblasts, odontoblasts, and some by endothelial cells. Collagen type IV in the basement membrane is synthesized by epithelial and endothelial cells.

• Reticular fibers: Constructed from units of collagen fibers, with periodic transverse striations. Reticular fibers appear black when stained with silver impregnation methods.

• Elastic fibers: Yellow in fresh tissue. When stained with resorcin-fuchsin, elastic fibers appear red; when stained with aldehyde fuchsin, they appear dark blue, and with orcein they appear black.

IV. Cells of Connective Tissue

• Fibroblasts: The main cells of connective tissue, responsible for synthesizing the components of the ground substance and connective fibers.

• Adipocytes: Specialized for fat storage.

• Mast cells: Play a role in inflammation and allergic reactions.

• Lymphocytes: Immune cells, responsible for protecting the body.

• Macrophages: Phagocytic cells, responsible for removing dead cells, bacteria, and foreign bodies.

V. Functions of Connective Tissue

Connective tissue performs many important functions in the body:

• Support and protection: Provides a framework for the body, protects other organs and tissues.

• Connection: Connects tissues and organs together, forming body systems.

• Nutrition: Supplies nutrients and oxygen to tissues and organs.

• Immunity: Protects the body from disease-causing agents.

• Circulation: Participates in the circulation of blood and lymph.

• Repair: Regenerates damaged tissue.

Note:

• Chondroitin sulfate: Is not a collagen fiber. It is a type of GAG.

• Collagen type IV: Is not a collagen fiber. It is a specialized type of collagen that plays a role in forming the basement membrane.

• Laminin: Is not a product of epithelial and endothelial cells. It is a type of glycoprotein synthesized by these cells.

• Thrombospondin: Is not only produced by platelets, but also synthesized by endothelial cells, fibroblasts, and smooth muscle cells.

This article needs to be supplemented with information about the types of proper connective tissue, cartilage, bone, as well as the function of each type of tissue.